Metronidazole Use in Infants
Yes, metronidazole can be given to infants, including neonates, but requires careful age-based dose adjustments due to prolonged drug half-life and accumulation risk in this population. 1, 2, 3
Age-Specific Dosing Algorithm
For Term and Late Preterm Infants (≥34 weeks gestational age)
- Intravenous dosing: 7.5 mg/kg every 12 hours (not every 8 hours as in older children) for infants in the first weeks of life. 1, 2, 3
- Oral dosing: 30-40 mg/kg/day divided into doses given every 12 hours when oral therapy is appropriate. 4
For Preterm Infants (<34 weeks gestational age)
- Dosing should be based on postmenstrual age (gestational age + postnatal age), with longer intervals between doses due to even more prolonged elimination. 5
- Consider 7.5 mg/kg every 24-48 hours for very premature infants, though specific guidelines vary. 5
Critical Pharmacokinetic Considerations
- Neonates have a metronidazole half-life of 22-23 hours, approximately twice that of adults, necessitating less frequent dosing to prevent drug accumulation. 2, 3
- Drug levels rise progressively over the first 3 days of therapy before reaching steady state, with peak concentrations after the final dose being approximately double those after the first dose. 2, 3
- Infants <7 days of age show higher drug levels than older infants at the same dose, requiring particular caution in the first week of life. 2
- Septicemic neonates show continually rising levels rather than reaching a plateau, suggesting even greater caution in critically ill infants. 2
Approved Indications in Infants
Complicated Intra-Abdominal Infections
- Metronidazole is used off-label but safely in late preterm and term infants (≥34 weeks gestation) with complicated intra-abdominal infections to provide anaerobic coverage. 1
- In a multicenter trial of 55 infants (median gestational age 36 weeks, median postnatal age 7 days), combination therapy including metronidazole achieved 96% therapeutic success with minimal adverse events. 1
- Only one adverse event (candidal rash) was potentially attributable to metronidazole in this cohort. 1
Anaerobic Infections
- Metronidazole is effective for soft tissue abscesses, aspiration pneumonia, intracranial abscesses, and chronic sinusitis caused by anaerobic organisms in pediatric patients. 4
- 93% of anaerobic isolates (including Bacteroides species) had MICs ≤2 μg/mL, well below achievable serum concentrations. 4
Giardiasis
- For giardiasis in children ≥3 years, tinidazole is preferred, but metronidazole remains an alternative. 6
- Metronidazole is not FDA-approved for giardiasis treatment, though it is commonly used off-label. 6
- A pediatric suspension is not commercially available but can be compounded from tablets. 6
Safety Profile in Infants
- No serious local or systemic adverse reactions were noted in pharmacokinetic studies of neonates receiving metronidazole. 3
- In a cohort of 15 pediatric patients (including infants) treated for 14-52 days, no adverse reactions occurred and 14 of 15 achieved complete cure. 4
- 98% of infants in the cIAI trial were alive through 30 days post-therapy with high clinical cure rates. 1
Common Pitfalls to Avoid
- Do not use adult dosing intervals (every 8 hours) in neonates—this will cause drug accumulation and potential toxicity. 2, 3
- Do not assume steady-state concentrations are achieved immediately—levels continue rising for 3 days. 2, 3
- Avoid standard pediatric dosing (40-50 mg/kg/day divided every 8 hours) in the neonatal period; use 7.5 mg/kg every 12 hours instead. 2, 4, 3
- Monitor for feeding intolerance, which occurred in 33% of infants with complicated intra-abdominal infections. 1
Practical Dosing Example
For a 2-week-old term infant weighing 3.5 kg with suspected necrotizing enterocolitis: